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At least 1,117 records · Page 62Linked to original sources
PubMed2006

Postnatal allometry of the skeleton in Tupaia glis (Scandentia: Tupaiidae) and Galea musteloides (Rodentia: Caviidae)--a test of the three-segment limb hypothesis.

During the evolution of therian mammals, the two-segmented, sprawled tetrapod limbs were transformed into three-segmented limbs in parasagittal zig-zag configuration (three-segment limb hypothesis). As a consequence, the functional correspondence of limb segments has changed (now: scapula to thigh, upper arm to shank, fore arm plus hand to foot). Therefore, the scapula was taken into account in the current study of the postnatal growth of the postcranial skeleton in two small mammalian species (Tupaia glis, Galea musteloides). Comparisons were made between the functionally equivalent elements and not in the traditional way between serially homologous segments. This study presents a test of the three-segment limb hypothesis which predicts a greater ontogenetic congruence in the functionally equivalent elements in fore and hind limbs than in the serially homologous elements. A growth sequence, with decreasing regression coefficients from proximal to distal, was observed in both species under study. This proximo-distal growth sequence is assumed to be ancestral in the ontogeny of eutherian mammals. Different reproductive modes have evolved within eutherian mammals. To test the influence of different life histories on ontogenetic scaling during postnatal growth, one species with altricial juveniles (Tupaia glis) assumed to be the ancestral mode of development for eutherians and one species with derived, precocial young (Galea musteloides) were selected. The growth series covered postnatal development from the first successive steps with a lifted belly to the adult locomotory pattern; thus, functionally equivalent developmental stages were compared. The higher number of allometrically positive or isometrically growing segments in the altricial mammalian species was interpreted as a remnant of the fast growth period in the nest without great locomotor demands, and the clearly negative allometry in nearly all segments in the precocial young was interpreted as a response to the demand on early locomotor activity. Different life histories seem to have a strong influence on postnatal ontogenetic scaling; the effects of the developmental differences are still observable when comparing adults of the two species.

Aging↗
PubMed2001

Early identification of impaired myocardial reperfusion with serial assessment of ST segments after percutaneous transluminal coronary angioplasty during acute myocardial infarction.

To evaluate the relation between ST-segment analysis and microvascular reperfusion in patients with acute myocardial infarction (AMI), we studied 51 patients with first AMI who were successfully treated by percutaneous transluminal coronary angioplasty (PTCA). The lead showing the greatest ST-segment elevation on the 12-lead electrocardiogram (ECG) was serially investigated until 24 hours after PTCA. Successful reperfusion was determined by technetium-99m tetrofosmin single-photon emission computed tomography. Impaired reperfusion (group 1: < 4 change in the sum of the defect score from before to immediately after PTCA) was observed in 24 patients, and successful reperfusion (group 2) was observed in 27 patients. Although ST-segment elevation was reduced significantly at 30 minutes after PTCA in group 2 (2.2 +/- 1.4 to 1.7 +/- 1.3 mm, p = 0.01), there was no significant change in group 1 (1.9 +/- 1.9 to 2.4 +/- 1.7 mm). Ten of 14 patients (71%) with persistent ST-segment elevation (DeltaST > 0 mm change in ST segment from before to 30 minutes after PTCA > 0) were in group 1, whereas 23 of 37 patients (62%) with ST-segment resolution (DeltaST < or = 0) were in group 2. The sensitivity and specificity of persistent ST-segment elevation for predicting impaired microvascular reperfusion were 42% and 85%, respectively. Thus, persistent ST-segment elevation 30 minutes after primary PTCA was a highly specific electrocardiographic marker of impaired reperfusion in patients with AMI.

Aged↗
PubMed1997

Dobutamine-induced ST-segment elevation in patients with acute myocardial infarction and the role of myocardial ischemia, viability, and ventricular dyssynergy.

We analyzed the relation between dobutamine-induced Q-wave ST-segment elevation and regional contraction during low (5 to 10 microg/kg/min) and high doses (20 to 40 microg/kg/min) of dobutamine in a series of 391 dobutamine echocardiographic tests performed 10 +/- 2 days after a first uncomplicated acute myocardial infarction (AMI). ST-segment elevation was defined as > or = 1 mm new or additional J-point elevation with a horizontal or upsloping ST segment lasting 80 ms. Wall motion score index at rest was derived using a 16 segment-4 grade score model. Patients with dobutamine-induced ST-segment elevation had a higher wall motion score index at rest (anterior wall AMI: 1.67 +/- 0.27 vs 1.43 +/- 0.30, p = 0.0001; inferior wall AMI: 1.44 +/- 0.27 vs 1.30 +/- 0.18, p = 0.0001) and similar incidence and extent of myocardial viability and homozonal ischemia in comparison with those without ST-segment elevation. The sensitivity, specificity, and accuracy of dobutamine-induced ST-segment elevation for detecting residual homozonal ischemia were 51%, 55%, and 54%, respectively, in patients with anterior wall AMI, and 42%, 68%, and 58%, respectively, in patients with inferior wall AMI. In conclusion, dobutamine-induced ST-segment elevation is not associated with higher incidence and extent of viable or jeopardized myocardium but rather to a greater extent of wall motion abnormalities at rest. Thus, this finding does not represent a clinically reliable discriminator for selecting patients for coronary angiography and possible revascularization procedures.

Adult↗
PubMed1997

Quantitative evaluation of the segmental left ventricular response to dobutamine stress by tissue Doppler echocardiography.

Tissue Doppler imaging displays color-coded myocardial velocity on-line and has potential to objectively quantify regional left ventricular function. Sixty patients, aged 56 +/- 10 years, were studied to determine the normal and abnormal segmental endocardial velocity response to dobutamine stress, and the sensitivity, specificity, and accuracy of tissue Doppler imaging for detecting abnormal wall motion at peak stress as defined by routine visual interpretation. Separate 2-dimensional routine gray scale and color tissue Doppler image sets were acquired at rest and peak dobutamine stress in a digital cineloop format. Routine wall motion interpretation from gray scale images and color-coded peak systolic endocardial velocity from tissue Doppler images were determined independently. Twenty-two patients who reached their target heart rate and had normal wall motion at peak stress served as a control group. There were 19 patients who had wall motion abnormalities at peak stress. Segmental peak endocardial velocities increased significantly in all segments in the control group. Endocardial velocity was significantly lower at peak stress in the pooled abnormal segments than in the pooled normal segments: 3.1 +/- 1.2 versus 7.2 +/- 1.9 cm/s, respectively (p < 0.05 vs normal control). However, the velocity response of abnormal apical segments could not be distinguished from normal controls by tissue Doppler imaging. Excluding apical segments, a peak velocity of < or = 5.5 cm/s with peak stress had an average sensitivity of 96%, specificity of 81%, and accuracy of 86% for identifying abnormal segments at peak stress as defined by routine 2-dimensional criteria. Tissue Doppler imaging has the potential to quantify regional left ventricular function during dobutamine stress.

Adrenergic beta-Agonists↗
PubMed1997

Facet tropism in lumbar motion segments and its significance in disc herniation.

OBJECTIVE AND DESIGN: To define facet tropism (FT) for each motion segment of the lower lumbar spine for subjects without disc herniation, and to evaluate the significance of facet tropism in disc herniation. METHODS: Sixty subjects were evaluated by measuring the facet angle (FA) of three lower lumbar motion segments with the use of computed tomography (CT) and a computer program. The subjects were divided into two groups: 33 without disc herniation and 27 with disc herniation at one or more levels of lower lumbar motion segments. The FA was defined as the angle of the facet and midsagittal lines. The difference between the right and left FAs at each motion segment was calculated. FT was defined as an angle difference larger than the mean and one standard deviation of the angle differences between the right and left FAs at each motion segment in the group without disc herniation. OUTCOME MEASUREMENTS: Statistical significance of the bilateral angle difference of each lower lumbar motion segment between the two groups was analyzed by the two-sample t test. Using the defined angle difference for FT, the incidence of FT in the two groups at each motion segment was analyzed by the Fisher's exact test. RESULTS: FT was defined for the 33 subjects without disc herniation on CT scans as an angle difference larger than 12 degrees at L3-L4, 15 degrees at L4-L5, and 12 degrees at L5-S1, approximately. There was no statistical significance in the bilateral FA difference (p > .05) and incidence of FT (p > .05) at each segment between the two groups. CONCLUSION: This study did not show that facet joint tropism plays a significant role in disc herniation in the lower lumbar spine.

Adult↗
PubMed2002

Autonomous and heteronomous positioning of transmembrane segments in multispanning membrane protein.

Polypeptides synthesized by membrane-bound ribosomes are cotranslationally integrated into the endoplasmic reticulum membrane. Transmembrane segments are positioned in the membrane via two distinct modes. In the autonomous mode, hydrophobic segments are integrated into the membrane based on the characteristics of the segment. In the heteronomous mode, a segment that is not inserted into the membrane by itself is forced into a transmembrane disposition by other segments. This unexpected insertion is achieved by a signal-anchor sequence with N(exo)/C(cyto) topology that translocates the preceding segment. Structural and functional diversities of transmembrane segments in multispanning proteins are acquired via this mode. Such a heteronomous positioning of polypeptide segments might occur not only in the integration process of membrane proteins but also in the general folding processes of soluble proteins.

Endoplasmic Reticulum↗
PubMed2004

Longitudinal diffusion in retinal rod and cone outer segment cytoplasm: the consequence of cell structure.

Excitation signals spread along photoreceptor outer segments away from the site of photon capture because of longitudinal diffusion of cGMP, a cytoplasmic second messenger. The quantitative features of longitudinal diffusion reflect the anatomical structure of the outer segment, known to be profoundly different in rod and cone photoreceptors. To explore how structural differences affect cytoplasmic diffusion and to assess whether longitudinal diffusion may contribute to the difference in signal transduction between photoreceptor types, we investigated, both theoretically and experimentally, the longitudinal diffusion of small, hydrophilic molecules in outer segments. We developed a new theoretical analysis to explicitly compute the longitudinal diffusion constant, Dl, in terms of outer segment structure. Using time-resolved fluorescence imaging we measured Dl of Alexa488 and lucifer yellow in intact, single cones and validated the theoretical analysis. We used numerical simulations of the theoretical model to investigate cGMP diffusion in outer segments of various species. At a given time interval, cGMP spreads further in rod than in cone outer segments of the same dimensions. Across all species, the spatial spread of cGMP at the peak of the dim light photocurrent is 3-5 microm in rod outer segments, regardless of their absolute size. Similarly the cGMP spatial spread is 0.7-1 microm in cone outer segments, independently of their dimensions.

Animals↗
PubMed2002

Automated cerebrum segmentation from three-dimensional sagittal brain MR images.

We present a fully automated cerebrum segmentation algorithm for full three-dimensional sagittal brain MR images. First, cerebrum segmentation from a midsagittal brain MR image is performed utilizing landmarks, anatomical information, and a connectivity-based threshold segmentation algorithm as previously reported. Recognizing that cerebrum in laterally adjacent slices tends to have similar size and shape, we use the cerebrum segmentation result from the midsagittal brain MR image as a mask to guide cerebrum segmentation in adjacent lateral slices in an iterative fashion. This masking operation yields a masked image (preliminary cerebrum segmentation) for the next lateral slice, which may truncate brain region(s). Truncated regions are restored by first finding end points of their boundaries, by comparing the mask image and masked image boundaries, and then applying a connectivity-based algorithm. The resulting final extracted cerebrum image for this slice is then used as a mask for the next lateral slice. The algorithm yielded satisfactory fully automated cerebrum segmentations in three-dimensional sagittal brain MR images, and had performance superior to conventional edge detection algorithms for segmentation of cerebrum from 3D sagittal brain MR images.

Algorithms↗
PubMed1997

Identification of the minimum segment in which the threonine246 residue is a potential phosphorylated site by protein kinase A for the LukS-specific function of staphylococcal leukocidin.

Staphylococcal leukocidin and gamma-hemolysin consist of LukF and LukS for leukocidin and LukF and Hlg2 for gamma-hemolysin. In this report, we identify the minimum segment responsible for the LukS-specific function of leukocidin. After chemical analysis and homology study of the amino acid sequence of the C-terminal region between LukS and Hlg2, we found a unique 5-residue sequence I242K243R244S245T246 in LukS in which the 4-residue KRST is identical with that of the phosphorylated segment of a protein phosphorylated by protein kinase A. To elucidate whether the 5-residue segment is essential for the LukS function, we created plasmids containing a series of mutant genes corresponding to the 5-residue sequence and expressed them in Escherichia coli. The mutant proteins were purified and assayed for their leukocytolytic activity with LukF. The mutant MLS-TS, in which the T246 in the 5-residue sequence was replaced by S, showed leukocidin activity 10 times higher than that of the intact LukS. However, neither mutant MLS-TY nor MLS-TA, in which T246 was replaced by Y or A, respectively, showed leukocidin activity. The 5-residue segment was found to be deleted in Hlg2. The mutant of Hlg2, in which the 5-residue segment was inserted at the position that the segment is deleted, showed leukocidin activity. The boiled LukS, MLS-TS, and MHS-Z were strongly phosphorylated with [gamma-32P]ATP in the presence of protein kinase A in a cell-free system. Thus, we conclude that the 5-residue segment 1242K243R244S245T246 is the pivotal segment of LukS responsible for the LukS function of staphylococcal leukocidin.

Adenosine Triphosphate↗
PubMed1996

Laparoscopically assisted transvaginal segmental resection of the rectosigmoid colon for endometriosis.

OBJECTIVE: To compare three methods of segmental lower colon resection for treatment of symptomatic intestinal endometriosis. DESIGN: Retrospective case study. SETTING: Private practice patients in a rural community hospital. PATIENTS: Patients with nodular, invasive rectosigmoid endometriosis requiring segmental resection and anastomosis for treatment. Laparotomy patients were matched with laparoscopy patients for severity of intestinal endometriosis. INTERVENTIONS: Segmental resection of the rectosigmoid colon by laparotomy, by a laparoscopic Intracorporeal technique or by a laparoscopically assisted transvaginal technique. MAIN OUTCOME MEASURES: Length of surgery, length of hospital stay, operating room charges and total hospital charges corrected to 1995 dollars. RESULTS: Compared with laparotomy segmental colon resection for endometriosis, laparoscopic transvaginal segmental resection resulted in a shorter length of stay, equivalent operating room charges, and significantly lower total hospital charges. The laparoscopic transvaginal technique is much faster, safer, and less fatiguing to the surgeon than a total intracorporeal technique. CONCLUSIONS: Laparoscopically assisted transvaginal segmental rectosigmoid resection for endometriosis is a promising technique that is simpler than a laparoscopic intracorporeal segmental resection technique and is less costly than a laparotomy segmental resection technique.

Colon, Sigmoid↗
PubMed2003

Segmental tibial fractures: an assessment of procedures in 27 cases.

Twenty-seven patients (two women) with segmental tibial fractures (19 open) were treated in our institution with a mean age of 38.9 years (range 22-67 years) and a mean Injury Severity Score of 11.5 (9-34). Sixteen fractures were stabilised initially with an interlocking nail, seven with an external fixator, one with a hybrid external fixator, two cases were plated and one was treated in plaster. The mean size of the segment was 11.5 cm (range 4-20 cm). Soft tissue coverage was required in 17 cases. There were three cases of compartment syndrome, six cases of superficial infection and four deep infection cases (two of which required amputation). In four cases, excision of the non-viable segment was necessary. Overall, 13 patients were subjected to a second operative procedure (OP) (four external fixators were replaced with the AO solid tibial nail, two Ilizarov bone transports following excision of the dead bone segment, 2 below knee amputations, 3 exchange reamed nailings, 1 LISS plate application for stability and 1 ring fixator for compression of a fracture). Five patients underwent third procedure (two Ilizarov for bone transport, two exchange nailing, and one bone grafting). The mean time to union of the proximal segment was 38.8 weeks (range 10-78 weeks) and 41.4 weeks (range 12-65 weeks) for the distal segment, respectively. The treatment of segmental tibial fractures poses many problems to the surgeon due to the precarious blood supply of the intermediate segment. The risk of non-union delayed union, infection and additional procedures is high as seen in this series of patients.

Adult↗
PubMed2003

Influence of body segment parameters and modeling assumptions on the estimate of center of mass trajectory.

This study sought to determine the effect of inaccuracies in body segment parameters and modeling assumptions on the estimate of antero-posterior center of mass (COM) trajectory. Four different methods, one based on segmental kinematics, and three methods based on kinetic recordings were compared via simulation. Kinematic patterns (quiet stance, ankle-related sway, hip-ankle-related sway, sit-up and sit-up-sit-down) were tested with a 2D four-link model of the body and the ground reaction force vector was obtained by inverse dynamics. Errors in the estimation of body segment parameters were simulated by applying a +/-10% variation to one or more parameters at a time. These errors propagated differently to the COM estimated location between methods, between parameters within the same method, and between tasks. The kinematics-based method was the most sensitive to body segment parameters, with special regards to segment lengths and head-arms-trunk parameters. Root mean square error between estimated and simulated COM location reached 19mm in balance-related tasks and 38.3mm in sit-up-sit-down. The kinetics-based methods were largely less sensitive to inaccuracies in body segment parameters. In particular, the technique proposed by Zatsiorsky and King (J. Biomech. 31 (1998) 161), was completely insensitive to segment parameters. On the other hand the kinetics-based methods showed an intrinsic estimation error, due to the underlying model assumptions. The methods based on the double integration of horizontal force had better outcomes with tasks challenging such assumptions, with a maximal error in COM location of 15mm in the sit-up-sit-down. The method proposed by Shimba (J. Biomech. 17 (1984) 53) showed the best trade-off between sensitivity to body segment parameters and estimation performances given the ideal test conditions.

Biomechanical Phenomena↗
PubMed1997

Continuous ST-segment monitoring during coronary angioplasty using orthogonal ECG leads.

In order to characterize ST-segment shifts during transient coronary artery occlusion, 24 patients with single-vessel disease were continuously monitored during percutaneous transluminal coronary angioplasty by use of a computerized orthogonal lead system. Changes of ST-segment (J + 60 ms) in leads X, Y, and Z and of the ST vector magnitude were analyzed by using 20 microV as a threshold for significant ST-segment shift. The sensitivity and magnitude of this shift were compared among the left anterior descending, right coronary, and circumflex artery groups (11, 8, and 5 patients, respectively) during balloon inflation. Significant ST-segment shifts were seen in 22 patients (92%) in ST-VM, Y, and Z leads and all patients in lead X (100%). There was no significant difference in sensitivity of either the ST vector magnitude or the most sensitive lead for occlusion detection among the three groups. There was a significantly greater magnitude of ST shift during left anterior descending artery occlusion than during right coronary artery and circumflex artery occlusions in ST-VM. Analysis of the direction of ST shifts in the X, Y, and Z leads showed a characteristic pattern, which could distinguish among the three coronary groups in 21 patients (88%). The presence of collaterals was significantly associated with ST-segment depression in leads oriented toward ischemia (3 of 6 patients) as compared with ST-segment elevation in the absence of collaterals (all of 15 patients), P > .01. It is concluded that ST-segment shift in the orthogonal leads is a reliable marker for myocardial ischemia. It is equally sensitive to occlusion of each of the three major coronary arteries and can thus identify the occluded coronary. An ST-segment depression instead of an elevation was related to the presence of collaterals, which may reflect a lesser degree of ischemia.

Adult↗
PubMed1999

Ex vivo transfection of transforming growth factor-beta1 gene to pulmonary artery segments in lung grafts.

OBJECTIVE: Proximal pulmonary artery segment transfection may provide beneficial downstream effects on the whole-lung graft. In this study, transforming growth factor-beta1 was transfected to proximal pulmonary artery segments, and the efficacy of transforming growth factor-beta1 transfection was examined in ischemia-reperfusion injury and acute rejection models of rat lung transplantation. METHODS: In the ischemia-reperfusion injury model, orthotopic left lung transplantation was performed in F344 rats. In group I, the PPAS was isolated and injected with saline solution. In 2 other groups, lipid67:DOPE:sense (group II) or antisense transforming growth factor-beta1pDNA construct (group III) was injected instead of saline solution. After cold preservation at 4 degrees C for 18 hours, lung grafts were implanted. Graft function was assessed 24 hours later. In the acute rejection model, donor lung grafts were harvested. Proximal pulmonary artery segments were injected with saline solution (group I) or sense (group II) or antisense lipid gene construct (group III) and then implanted. Graft function was assessed on postoperative day 5. RESULTS: In the ischemia-reperfusion injury study, there were no significant differences in oxygenation, wet-to-dry weight ratios, graft myeloperoxidase activity, or transforming growth factor-beta1 levels in platelet-poor serum or proximal pulmonary artery segment homogenates. In the acute rejection study, oxygenation was significantly improved in group II receiving transforming growth factor-beta1 (group II vs I and III, 136.0 +/- 32.5 vs 54.0 +/- 9.6 mm Hg and 53.8 +/- 14.8 mm Hg; P =.016 and.016). There were no significant pathologic differences. Transforming growth factor-beta1 concentrations from proximal pulmonary artery segment homogenates in group II were significantly higher compared with controls. CONCLUSIONS: Ex vivo transfection of transforming growth factor-beta1 to proximal pulmonary artery segments did not affect reperfusion injury of lung isografts. In acute rejection, however, ex vivo transfection of transforming growth factor-beta 1 to proximal pulmonary artery segments improved allograft function. This suggests that transfection to proximal pulmonary artery segments exerts beneficial downstream effects on the whole-lung allograft.

Acute Disease↗
PubMed1994

Grafting of cultured uroepithelium and bladder mucosa into de-epithelialized segments of colon in rabbits.

Urinary tract reconstruction using bowel can result in acid-base and electrolyte abnormalities. We tested the feasibility of grafting bladder mucosa and urothelial cells grown on a biodegradable polyglactin 910 scaffold onto de-epithelialized segments of bowel in the rabbit. A segment of de-epithelialized colon was either grafted with cultured urothelium on a collagen mesh scaffold (12 rabbits) or with free bladder mucosa (11 rabbits). In 10 rabbits that served as a control group another segment of bowel was isolated and de-epithelialized. No urothelial or bowel epithelial growth was present 4 weeks later in 10 of the isolated de-epithelialized colonic segments grafted with the cultured urothelium. In 2 segments a minute focus of epithelium staining positively for anticytokeratin antibodies AE1 and AE3 was seen but this could not be histologically differentiated as either urothelium or native colonic epithelium. All 7 surviving animals that underwent a bladder mucosal graft had viable urothelium at sacrifice 30 days postoperatively. In 2 of the 7 rabbits microscopic nests of colonic epithelium were also found underneath the urothelial layer. Of the 7 internal controls 6 had no evidence of bowel epithelial regrowth 4 weeks after de-epithelialization. This study demonstrated that a confluent layer of urothelial cells could be grown in culture using a scaffold of biodegradable mesh and rat tail collagen. We also showed that bladder mucosal grafts can be grown on de-epithelialized bowel segments. We were unable to graft successfully cultured urothelial cells onto a de-epithelialized bowel segment. Further improvement in understanding the role of the submucosal matrix in cell growth may lead to future success in covering large segments of de-epithelialized bowel with autologous urothelium.

Animals↗
PubMed2002

Versatility of reconfigured-colon-segment technique for urinary reconstruction requiring use of tubular structures.

INTRODUCTION: When a colon segment is used for urinary reconstruction and a tubular structure is necessary, the option for the tubular structures is limited. We prepared a short colon segment in advance for creating a reconfigured tube. TECHNICAL CONSIDERATIONS: Short colon segments are separated beforehand from the edges of the main colon segment for a continent urinary reservoir or augmentation cystoplasty. The short segments are either reconfigured, if necessary, into tubular structures to produce a continent valve or to replace a ureteral defect or discarded if they prove not to be needed. The number of short segments can be predicted on the basis of the clinical situation before and during the operation. CONCLUSION: Preparation of short colon segments is useful for urinary reconstruction using a colon segment that might require a number of tubular structures. The technique provides versatility and flexibility in difficult clinical conditions.

Adolescent↗
PubMed2003

Low-complexity segments in Plasmodium falciparum proteins are primarily nucleic acid level adaptations.

Protein segments that contain few of the possible 20 amino acids, sometimes in tandem repeat arrays, are referred to as containing "simple" or "low-complexity" sequence. Many Plasmodium falciparum proteins are longer than their homologs in other species by virtue of their content of such low-complexity segments that have no known function; these are interspersed among segments of higher complexity to which function can often be ascribed. If there is low complexity at the protein level, there is likely to be low complexity at the corresponding nucleic acid level (departure from equifrequency of the four bases). Thus, low complexity may have been selected primarily at the nucleic acid level and low complexity at the protein level may be secondary. In this case, the amino acid composition of low-complexity segments should be more reflective than that of high complexity segments on forces operating at the nucleic acid level, which include GC-pressure and AG-pressure. Consistent with this, for amino acid determining first and second codon positions, open reading frames containing low-complexity segments show increased contributions to downward GC-pressure (revealed as decreased percentage of G+C) and to upward AG-pressure (revealed as increased percentage A+G). When not countermanded by high contributions to AG-pressure, low-complexity segments can contribute to base order-dependent fold potential; in this respect, they resemble introns. Thus, in P. falciparum, low-complexity segments appear as adaptations primarily serving nucleic acid level functions.

Amino Acids↗
PubMedDate not supplied

Prognostic implications of evaluation of contractile reserve in akinetic and hypokinetic segments during low dose dobutamine echocardiography in patients with acute myocardial infarction.

BACKGROUND: Previous studies have reported the prognostic value of myocardial viability (MV) detected using low-dose dobutamine echocardiography (DbE). However, viability was frequently evaluated as improvement in regional wall motion score index, which includes increased function in hypokinetic segments, in which viable myocardium is necessarily present. It is not known whether an evaluation focusing on akinetic segments, in which the possible presence of viable myocardium is unknown, might have more prognostic value. The aim of this study was to compare the prognostic value of the improvement of myocardial function during dobutamine infusion in akinetic and hypokinetic regions in patients with acute myocardial infarction (AMI). METHODS: 191 patients with uncomplicated AMI and at least one akinetic segment were retrospectively selected from those consecutively examined at our echo-laboratory to evaluate MV using DbE. Myocardial viability was evaluated both as an increment in RWMSI (Delta RWMSI), which takes into consideration improvement in both akinetic and hypokinetic regions, and as an improvement of function in akinetic (Delta akinetic) and hypokinetic (Delta hypokinetic), segments considered separately. Follow-up evaluation was performed at 30+/-13 months. RESULTS: On the basis of the Delta RWMSI, 94/191 patients were judged to have myocardial viability, whereas considering myocardial viability in akinetic segments only, 72/191 patients showed viability. At follow-up 18 patients had died (six viable considering Delta RWMSI; three viable considering Delta akinetic). The presence of a previous AMI, the site of AMI, RWMSI and the number of akinetic segments, and Delta RWMSI and Delta akinetic were related to mortality at univariate Cox analysis. At multivariate stepwise Cox regression analysis Delta akinetic, but not Delta hypokinetic proved to be significantly related to mortality. The Kaplan-Meier survival curves were no different in patients with or without viable myocardium evaluated as Delta RWMSI, while they were significantly different considering patients with or without viability in akinetic segments (P=0.04). CONCLUSION: In conclusion our study confirms the prognostic importance of the evaluation of myocardial viability in infarcted patients. However, it points out that it is the presence of viability in akinetic segments that affects long-term survival in these patients. This supports the hypothesis that other mechanisms, above and beyond the effect on regional wall motion, are involved in the beneficial effects of myocardial viability.

Aged↗